A wide range of minimally invasive methods, for example x-ray methods, for imaging an organ are known in modern medicine. The object of these methods is essentially to obtain comprehensive knowledge about the respective organ and its state without opening up the body. In a known application for example a C-arm of an x-ray device with an x-ray tube and an x-ray detector is rotated at constant rotation speed or angular velocity o through an angle of 300 degrees for example around a patient, generally about the longitudinal axis of the body. Instead of just a local view through a catheter using a camera, etc. such imaging methods and a corresponding device can be used to acquire a number of individual recordings of the organ in question from different spatial directions, on the basis of which three-dimensional images or other representations, such as any sections in particular, can ultimately be produced. Such methods can be used to examine the cardiac muscles and coronary vessels for example without a catheter.
For a 3D reconstruction however only the images that show the organ in the same respective state can be used. In a preferred and extremely important application, the recording of the heart, the filling phase or diastole is selected as the representation state, being a relative rest phase of the heart. In the case of a living human being this rest phase lasts for less than 200 milliseconds even in a rest position during relaxation. During recording however only a few projections can be collected for 3D reconstruction and modeling in a time window in the above-mentioned cardiac rest phase. The data collected outside the recording time window or outside the cardiac rest phase of relevance to the examination respectively cannot be used for imaging because of the movement of the heart. Such data losses result in large gaps in the projection angle space and therefore an incomplete representation base for the organ as a whole. Interpolations can perhaps be made with relatively uncertain assumptions within these representation gaps. A similar problem also arises with other organs, the form and/or position of which changes over time. However in order to keep the overall radiation load low, where the x-ray tube is in constant operation, the recording device cannot rotate at any slow rotation speed that may be required to obtain as many recordings as possible from different spatial directions at favorable recording times. Nor is it possible for a measurement to be repeated any number of times for the same reason.
It is therefore proposed in U.S. Pat. No. 6,324,254 B1 for recording a rhythmically moving vessel that the C-arm be moved at the slowest possible rotation speed, preferably less than 2 degrees per second, but taking individual image recordings, triggered by the vessel movement or an organ movement causing the vessel movement. In other words radiation is only emitted from the x-ray tube and a recording is only taken at specific times, while the C-arm moves around the patient at the slowest possible constant speed. The constant rotation speed is hereby established before measurement, preferably as a function of the frequency of the rhythmic vessel or organ movement, to ensure that a minimum number of recordings can be generated during a measurement. However this procedure has the disadvantage that the measurement takes a relatively long time. During this time it has to be ensured that the patient lies absolutely still. Even minimal position changes can cause the measurement to be impaired.
A similar method is proposed in U.S. Pat. No. 6,370,217 B1 for the measurement of a periodically moving object using a computed tomograph. During a measurement using such a computed tomography system the x-ray tube rotates at very high speed, for example at a speed in the order of approximately 1 second per rotation, a number of times around the patient. In order always to record the cyclically changing object in the same state in this process, there is also a control system here, triggered by the movement cycle, for when the x-ray tube emits short bursts of x-ray radiation to take individual recordings. Here too a constant rotation speed is preferably established before measurement as a function of the frequency of the rhythmic vessel or organ movement. The rotation speed is thereby adjusted such that where possible recordings can be generated from all spatial directions during a measurement. This method cannot however be used for a measurement with a C-arm or similar recording facilities, as, unlike with the significantly more complex structure of a computed tomography device, with such a relatively simple recording device the x-ray tube and detector cannot move at any speed and frequency around the patient. Generally only a rotation angle of maximum 300 degrees is available.
In the unexamined German application DE 103 36 278 A1 a method is disclosed for imaging an organ of the human or animal body by means of a recording device rotating through an angle, wherein the rotation speed of the rotating recording device is modulated as a function of a reference signal, which represents a current movement state of the organ to be imaged. Additionally or alternatively the measuring interval, with which the organ is recorded during the rotation, is adjusted by means of the reference signal to the duration of the movement cycle of the organ to be imaged. A corresponding device for implementing such a method is also described. One disadvantage of this method is that either angle ranges are passed through, for which no recordings are taken, or an acceleration phase of the recording device occurs at the start and end of each cycle.